Difference

The first sentence suggests that the theatre is not open at the moment; it is locked for the time being. Chances are, it will open little later. It has not been closed permanently.

The second sentence, on the other hand, seems to suggest that someone has forcibly closed down the theatre. Perhaps the municipal authorities were unhappy with the safety features and decided to shut the place down. In this case, the closure is either permanent or for a lengthy period of time.